This invention relates to a computer system, or storage network system, that can be run despite a failure in a host computer.
Some storage systems have host computers and storage on plural sites so that the extent of failure from a disaster is limited as much as possible and the business can be resumed quickly.
Large-scale natural disasters, terrorist attacks and the like can cause a serious damage to the building or even the entire city where a site of a storage system is located (regional disaster). In anticipation for such disasters, host computers of a storage system are set up across long distances and, when a failure occurs in one of the host computers, running of the system is handed over to another site.
In an example of such systems, two data centers on neighboring sites are connected to each other by a synchronous transfer copy function. One of the two data centers is connected to a third data center on a remote site by an asynchronous remote copy function, and the third data center holds data of a storage subsystem on the near site while keeping the order in which the storage subsystem has received the data from a host computer. Another example is a wide-area data storage system which gives each storage subsystem a function of tracking the progress of data transfer, reception and update between storage subsystems of two data centers where, in normal running of the storage system, direct data transfer does not take place (see JP 2001-175681 A).
A case is considered a case where a regional disaster causes a failure in the operating data center of a storage system of related art. The running of the storage system is switched over from the former operating data center to a remote data center. The switching over is called fail over.